Many display systems are being used to display different types of source images such as those generated by office software applications, video games, movies, etc. For these different types of source images, there are different luminance levels for display. For example, office applications (e.g., word processor) and video games are two difference extremes. In office applications, typically a very bright display screen relative to the background is not desired, whereas in entertainment applications such as video games user prefer visual effects of a bright display screen (higher luminance level) relative to the background. Conventionally, for displays such as LCD and Plasma, perception of higher level of luminance is achieved by increasing the power output of the display backlight. However, a bright backlight is expensive and consumes high power. Other schemes involve changing the ambient lighting intensity and color tone based on the image being displayed to enhance perception of the image relative to the ambient lighting. Yet other schemes monitor the ambient light and change display intensity accordingly. However, such techniques are often ineffective and further require additional hardware to achieve any results.
Further, conventional displays are limited to 8 bits of color depth, even when using spatial or temporal dithering to enhance color depth. Displays that can display more than 8 bits of color depth are problematic because the levels above 8 bits are very close together in voltage terms whereby any noise causes a cross-over leading to artifacts. In addition, mainstream digital interfaces (e.g., DVI, HDMI, etc.) cannot conveniently utilize more than 8 bits for color depth for display.
Another shortcoming of conventional displays systems such as LCD and Plasma (relative to CRTs) is that the maximum luminance in such displays cannot be selectively enhanced depending on the source image, whereby image contrast suffers. CRTs use an overdrive technique for enhancing luminance, wherein for example, in case of bright transitions in an image from back to white, the overdrive technique causes transitions from black to superwhite to provide the visual impact of very high contrast due to a very sharp transition. LCD displays do not provide such capability and resort to a very bright backlight for contrast. However, a bright backlight is expensive and consumes high power. Plasma displays drive the display harder for higher contrast ratio, resulting in higher power consumption, cost and shorter display life.
Yet another problem with LCDs is their relatively slow pixel state transition (slow temporal response characteristics) relative to that possible in CRTs. The slowness causes undesirable artifacts such as blurring and ghosting for fast moving objects in images (e.g., sports, games, etc.). The relative slow switching time (response time) of LCD displays coupled with the fact that conventionally each pixel is ‘on’ at an essentially constant luminance value until the information content of that pixel changes, generates various forms of motion artifact particularly when there is fast moving image content (e.g., movie chase scenes, sports, games, etc). A conventional approach for reducing the motion artifacts relies on breaking the “essentially constant luminance” value of each pixel (over a short time period) into a series of light pulse, by turning all pixels ‘off’ (i.e., a black screen) during alternate frames so that the luminance from each pixel is constantly turning ‘on’ and ‘off’. However, this causes considerable flickering of the displayed images unless LCD display is operated at a higher frame rate than normal which requires non-standard design at a higher cost.